Stop for a minute and take a close look at the air we breathe. OK, so you can't see it, and most of us walk around without giving it a second thought, but air is one of those critical things that helps plants and humans sustain life. It's also one of two critical components in the production of horse-power, the second being fuel.

Naturally, air and fuel must be supplied to each cylinder in the correct proportion and at the proper time, but hot rodders have taken to the task of creating additional power by improving airflow with aftermarket induction components. As we've said time and again, once airflow is improved, additional fuel is required, but the first item on the horsepower priority list should always be more air.

If you're an avid reader of MM&FF, the connection between airflow and horsepower should come as no surprise. That additional airflow can produce more power is hardly a revelation; the difficulty comes from how to actually go about improving it. When it comes to airflow, we're most concerned about the big three: the intake manifold, the cylinder heads, and the camshaft. Given the dynamic equation that is an internal combustion engine, the displacement, carb, and header sizing all play a part in the eventual power. But it's the intake, cam, and cylinder heads that determine the eventual power output and the overall shape of the power curve.

Though all of the components are covered in this buildup, we'll concentrate most of our efforts on the heads, more specifically the Pro 1 CNC aluminum cylinder heads from Dart.

A recent introduction by Dart, the Pro 1 CNC heads for the Ford Windsor family (including the 5.0L Mustang) offer a number of important features designed to help improve the flow characteristics. Checking out the impressive Pro 1 castings, the first thing you'll notice is its lightweight aluminum (355 T6) casting. This helps performance by improving the all-important power-to-weight ratio. Who wouldn't want the improved acceleration, handling, and braking associated with dropping a good 45-50 pounds off the nose of your Mustang?

Along with the weight savings, the aluminum helps raise the detonation threshold. Credit the heat dissipation qualities of aluminum for the reduced sensitivity to detonation. The final consideration-one you hope you never have to take advantage of-is the ease of repair. Damaged aluminum heads are more easily repaired than their cast-iron counterparts. We obviously never set out to hole a piston or torch a combustion chamber, but it does happen, and it's nice to know that such damage is much more easily repaired on an aluminum head than its cast-iron counterpart.

All the features of the aluminum construction are nice, but aluminum heads for 5.0L motors are a dime a dozen. What really makes the Dart Pro 1 heads attractive is the airflow potential offered by the CNC porting program. For the uninitiated, the acronym CNC means computer numeric con-trolled, basically a fancy name for computerized porting. Computer-controlled porting allows for precise, consistent machine work, and this translates into time savings and consistency between ports, even over dozens or hundreds of heads. The art of hand porting takes years of experience to master, and short of the tedious procedure of porting and flow testing each runner numerous times during the process, it's difficult, if not impossible, to replicate identical flow characteristics for each port.